Railroads maintain a vital position in the transportation of goods and, to a lesser extent, passengers. The maintenance of the current rail system and the establishment of new rail lines requires a continuous source of new railroad rails.
Traditionally, rails were manufactured in sections that were about 39 feet long. This length was arrived at simply due to the length of the train cars that carried the rails to the site of installation. At the site, the rail sections were bolted together. The use of these short rail sections and the unevenness created by the bolted attachment caused several problems. In the first place, the discontinuous rails made for a very rough ride. More importantly, the rough ride leads to increased rail wear and limits the maximum speed that trains can achieve on the rails. Bolting the rail sections together at the site also is a time-consuming and expensive process.
More recently, it has become standard practice to weld the rails sections together, rather than to bolt the sections together. The continuous welded rails give a substantially smoother ride and, therefore, lead to more durable rails. Along with the advent of rail welding, it became a common practice for the rail manufacturer, railroad or subcontractor to weld rail sections together into a relatively long ribbon at the manufacturing site. It is typically the current practice to have rail sections--from 39 feet to up to 100 feet or more--welded into quarter mile long ribbons. Special railroad cars are used to deliver the welded ribbons to the rail installation site. The welded ribbons are then either bolted or welded to one another at the installation site.
This practice has great advantages in both efficiency and superior rail quality when compared with the traditional bolting process. However, this method still has several disadvantages. Although the weld junctures used to join the short sections into quarter mile ribbons provide a smoother surface and last longer than the bolted attachment, the weld sites remain the weakest points on the rail since they have the discontinuity of the weld and also retain a softened segment on each side of the weld with non-desirable metallurgical properties. The welding process also requires a separate facility at which the shorter rail sections are prepared before welding, and are ground flush, straightened and inspected for integrity after welding.
There are no descriptions in the prior art or actual examples of non-welded unitary ribbons that approach the length of the welded ribbons currently in use. As mentioned above, rail sections are typically manufactured in lengths varying from 39 to 100 feet or more, and then are welded into the long ribbons.
In current practice, rail production includes the following steps: (1) bloom formation, (2) bloom reheating, (3) reverse rolling of the bloom to form a blank, (4) reverse rolling of the blank to from a rail, (5) cooling and straightening of the formed rail, (6) inspection of the rail, and (7) heat treatment of the rail to give superior wear characteristics.
Bloom formation is accomplished either by continuous casting or by ingot casting and breakdown rolling. In the typical arrangement, bloom formation is done at a discrete location from the rail rolling facility, and the bloom is allowed to cool before being rolled so that it must be reheated before being rolled. Some processes include rapid transport to final rolling so that the blooms do not cool and do not require reheating.
The bloom is heated to approximately 2250.degree. F. and subjected to a series of "rolling" treatments. The rolling consists of passing the malleable bloom between large rollers that exert significant pressure on the metal in order to elongate and shape the incipient rail. A critical factor in rail formation, is that the end product is not symmetrical about the horizontal axis. In order to obtain the asymmetrical rail, the bloom must not only be rolled in order to achieve the proper shape, but attention must be given to the internal stresses created within the metal due to the asymmetric rolling process.
The bloom is rolled in a "pass" through a rolling station until the entire section has passed between the rollers. The direction of movement of the bloom is then reversed, and the bloom will pass back through the same roller station. Depending on the type of roller station employed, the bloom may go between the same roll groove, or a different roll groove exerting pressure on different sections of the bloom. The bloom may undergo up to 10 to 12 passes at a single rolling station before proceeding to the next rolling station. This back and forth process is commonly referred to as "reverse rolling." After proceeding past the first rolling station, the incipient rail is often referred to as a blank.
The blank will pass from rolling station to rolling station in this back and forth manner until the final rail is formed. In addition to rolling stations, the typical rail manufacturing process will include both edgers and end cutters to provide a useable rail form.
After proceeding through the final rolling station, the rails will be subjected to a controlled cooling process. The controlled cooling will often include the asymmetric application of cooled air, water or a combination of both to the rail in order to prevent gross distortion of the rail as it cools. The different portions of the asymmetric rail, which has a head, a base and web portions, will naturally tend to cool at different rates. Because of the differential rates of cooling in the different sections of the rail, if the rail is allowed to cool in a non-controlled environment significant rail bowing or arching will occur.
During the reverse-rolling processes currently used to produce rails, considerable attention is paid to the ends of the incipient rail. As the end of the blank exits a given roller station considerable energy is applied to the metal through the rollers, and it is quite common that this will lead to some end distortion. Since the blank must enter between the rapidly spinning rollers on each pass through a rolling station, if the end is sufficiently deformed it is possible that the blank will not enter the roller properly and the entire process will be halted. In as many as three places in the process, it is necessary to cut off the ends of the bloom or blank in order to obtain a properly formed end.
Due to the nature of the reverse rolling process, it is impossible to produce very long rails. In each pass through a rolling station, the rollers must be set so that a uniform cross-sectional deformation is produced throughout the entire length of the blank. If there is a temperature gradient from one end to the other in the rail, the malleability will also vary and the uniform deformation will not be achieved. Such temperature gradients are inherent in reverse rolling long products.
An advantage of the reverse rolling process is that the rail can be manufactured in a relatively small area utilizing only a few rolling stations. Of course, the numerous reverse passes of the process cause significant delays in the production, as only one blank is rolled at a rolling station at a time.
Examples of disclosures that discuss the formation of rails using reverse rolling processes are in U.S. Pat. Nos. 4,301,670 of Engel and 4,344,310 of Kozono. In U.S. Pat. Nos. 3,342,053 of Stammbach and 4,503,700 of Kishikawa, processes that are referred to as "continuous" for producing rails are described. However, neither of these patents describes a truly continuous process. In both the Stammbach and Kishikawa patents, reverse rolling occurs in at least the blank formation stage.
U.S. Pat. Nos. 3,310,971 of Motomatsu and 3,555,862 of Yoshimo both describe processes for the continuous rolling production of large cross section steel products. Neither of the patents suggest the use of their process to produce asymmetric rails.
Takeuchi U.S. Pat. No. 4,820,015 discloses a continuous casting process for the formation of composite metal material. This continuous casting process is used in one embodiment to form a bloom that would be used for rail production. Takeuchi does not suggest that the continuous casting process be coupled with a continuous rolling process to form steel rails.
None of the above references teaches the manufacturing of rails that are unitary, non-welded and about one quarter mile long. Further, none of the above references teaches the manufacturing of rails utilizing a truly continuous rolling process. "Continuous rolling," as used herein, means a process wherein the malleable steel is successively passed through one rolling station after another without reversing, and various sections of the same incipient rail are simultaneously being rolled at more than one rolling station.
Finally, none of the above references teaches a process for the production of rails wherein different sections of a given blank are being rolled and cooled simultaneously.